Conventionally in an automatic transmission, gear shifting is effected one by one in order to avoid complicated multiple gear shifting (for example, speed change establishing fourth speed gear from second speed gear without establishing third speed gear). In such an automatic transmission, the next gear shifting is permitted only after determination has been made of the completion of previous gear shifting. It is therefore necessary to determine completion of gear shifting at an appropriate time.
Japanese Patent Laying-Open No. 2000-97331 discloses an automatic transmission that can properly determine the completion timing of inertia phase control. The automatic transmission disclosed in the publication of Japanese Patent Laying-Open No. 2000-97331 includes an input shaft receiving driving force from a driving mechanism, an output shaft transmitting the driving force to the wheels, a plurality of engagement elements setting the motive power transmitting characteristics between the input shaft and the output shaft, a detection unit detecting the revolution of the input shaft and the revolution of the output shaft, and a control unit controlling the release and engagement of a friction engagement element. The control unit determines that the friction engagement element has been sufficiently engaged to end the inertia phase control when a state of the gear ratio calculated based on the revolution of the input shaft and the revolution of the output shaft detected by the detection unit synchronizing with the gear ratio to be achieved by gear shifting continues for at least a predetermined determination time. The gear ratio is the value of the input shaft revolution divided by the output shaft revolution.
The automatic transmission disclosed in this publication is configured to end the inertia phase control at an elapse of a predetermined determination time for a state in which the gear ratio synchronizes with the gear ratio to be achieved. Accordingly, the inertia phase control can be continued even in the case where the gear ratio temporarily synchronizes with the gear ratio after gear shifting due to reduction in the engine speed, for example. The inertia phase control is terminated only when the synchronizing state continues for at least the predetermined determination time and the friction engagement element of the engagement side establishes sufficient engagement. Therefore, occurrence of gear shifting shock can be suppressed. By monitoring the gear ratio synchronizing time, determination of ending the inertia phase control can be made appropriately.
In the automatic transmission disclosed in the aforementioned publication, the next gear shifting will not be permitted unless the synchronizing state continues for at least the predetermined determination time in the case where gear shifting is set to be effected one gear at a time to obviate multiple gear shifting. There was a problem that the time required to eventually complete gear shifting becomes longer when gear shifting of a plurality of shifts is to be effected.